1. Field of the Invention
The present invention relates to a battery module, and more particularly, to a battery module having an improved coupling structure.
2. Description of the Related Art
Recently, a high output rechargeable battery (hereinafter referred as “unit battery”) using nonaqueous electrolyte having high energy density has been developed. A battery module having a plurality of unit batteries is used as a power source for driving motors, such as those of hybrid electric vehicles.
Depending on their external shape, unit batteries may be classified into different types, for example, prismatic and cylindrical types. The prismatic type unit battery includes an electrode assembly having positive and negative electrodes and a separator interposed between the positive and negative electrodes, a case for receiving the electrode assembly, a cap plate for sealing the case, and positive and negative terminals extending from the cap plate and electrically connected to the positive and negative electrodes, respectively.
Unit batteries are arranged in series to form a battery module. Adjacent batteries in the battery module are connected by a connecting member. More specifically, each of the negative and positive terminals is typically provided with a screw hole to which a nut member is screw-coupled. The nut members of the negative and positive terminals are connected by the connecting member.
A pair of end plates are typically arranged on outermost side portions of the unit batteries and restraint rods are coupled to the end plates. Therefore, the unit batteries are fixedly pressed and assembled by the end plates.
In conventional battery modules, unit batteries are assembled with each other merely in compression by coupling pressure generated by the restrain rod. Thus, the assembled unit batteries can be easily decoupled when an external force is applied thereto.
Additionally, in a conventional battery module, cell barriers may be provided between the unit batteries to define a flow channel for a heat transfer medium such as cool air. The cell barriers are typically spaced apart from each other by a constant distance to properly define the flow channel.
However, when the structure of the unit batteries varies due to external force, the distance between the cell barriers also varies, thus disrupting the flow channel. In this case, the temperature of the unit batteries excessively increases since the heat transfer medium cannot effectively pass through the unit batteries, causing malfunction of the battery module.